Oil well drilling procedures are now well developed and known. Typically, a rotating string of drill pipe, composed of individual sections (also called "joints") of drill pipe each typically 30 feet in length, carries at its lower end a drill bit which bores into the earth. As the bit bores deeper, additional joints of pipe are added to the string. Until relatively recently, the drill string typically was rotated about its axis by use of a rotary table located on a drilling platform in combination with a special section of drill string called a kelly joint or, more simply, a kelly. The rotary table typically is located in the platform floor directly below the path of vertical movement of a traveling block suspended in a derrick erected over the platform. The kelly is a non-round, often hexagonal, section of heavy-wall drill pipe, typically 42 feet in length, which forms the uppermost section of the drill string during drilling operations using a rotary table. The rotary table includes a power driven annular collar configured to slidably mate with the non-round configuration of the kelly, thereby to rotate the drill string and to power the drill bit.
When drilling with a rotary table and a kelly, the pipe string is drilled "kelly down", i.e., the length of the kelly joint, after which the kelly is raised above the rotary table. The drill string then is secured from downward movement in the rotary table, and the kelly is disconnected from the drill string. An additional 30 foot joint of drill pipe is added to the string and the kelly is then reconnected to the drill string. The string then is lowered through the rotary table to enable the kelly to engage, adjacent its lower end, in driving relation to the rotary table collar. Drilling operations are then resumed and continued to extend the well bore another 30 feet or so, at which time it is necessary to add another joint to the drill string. A new joint of drill pipe is added to the drill string each time the well bore is extended 30 feet or so, and each such addition requires performance of the operations described above.
In connection with oil and gas well drilling by use of rotary table equipment, additional features of the drilling equipment were developed, notably a mousehole and a rathole. A mousehole is a substantially vertically disposed tubular sleeve located in the drilling rig with its upper end at the platform closely adjacent the rotary table center. The mousehole is used to hold the next joint of drill pipe which is to be added to the drill string. The rathole is a somewhat larger diameter and often longer length tubular sleeve or the like also located in the drilling rig floor; it serves as a receptacle for the kelly.
Recently, a form of mechanism different from a rotary table has gained widespread acceptance in the oil and gas drilling industry for rotating a drill pipe string. That new equipment is known as a top drive. A top drive drilling mechanism and related equipment is supported by and below the traveling block for movement vertically along the well bore axis and for connection directly to the drill string. The top drive mechanism includes a motor, such as a DC electric motor, which operates to turn a coupling to which the upper end of the pipe string can be connected. Use of top drive drilling procedures eliminates the need for the long kelly joint and the need for disconnecting the kelly joint from the drill string each time it becomes necessary to increase the length of the drill string. Also, drill pipe can be added to the drill string in units of two or three joint "stands", i.e., multi-joint increments of drill string 60 or 90 feet in length, with a corresponding reduction in man hours expended in drilling a well of specified depth.
To take advantage of the drilling efficiencies obtainable with top drive systems, it is now appropriate to make-up double or triple (thribble) joint stands of drill pipe while drilling operations are in progress. However, commercial drilling rigs are not normally equipped to do this effectively, and so the pipe joints are made up into stands manually using hoists, chains and tongs developed for use in rotary table drilling procedures. Frequently the task of making up double or thribble stands of drill string cannot be completed fast enough to keep up with drilling, and so the efficiencies possible from use of top drive drill procedures are not being fully realized.
A problem commonly encountered when making up doubles and thribbles for top drive drilling is to ensure proper alignment of the tool joint ends. Each joint has an externally threaded coupling moiety at one end, called a "pin", and a cooperating internally threaded coupling moiety called a "box", at its other end. Drill strings typically are assembled with each joint in the string joint disposed pin end down. Because the travelling block in a drill rig derrick generally cannot be moved laterally in the derrick, a reserve pipe held in a mousehole must be angled for positioning to a joint suspended by the travelling block or by other hoists located other than directly vertically above the mousehole. Thus, stand make-up procedures cannot take advantage of gravity to obtain proper alignment between individual pipe joints being assembled to define a stand. Oil and gas well drill pipe is heavy and thus is difficult to handle manually. Misalignment of the pin and box ends of adjacent joints can slow the task of making up a stand and can lead to galling or other thread mutilation conditions. Additional problems encountered include applying the proper amount of torque to one or the other of the joints being connected by use of chain tongs. Usually, overall torque is measured only when the double or thribble is attached to the top drive unit, and there is no measurement or control of torque at each connection between joints in the stand.
U.S. Pat. No. 3,293,959 to Kennard discloses a pipe support well tool. The device is mounted over the rathole on a drilling platform. A housing includes a means for supporting a length of pipe to be added to the drill string and clamping means for securing the pipe from rotation during make-up with the kelly joint. The housing is mounted on spring legs such that the pipe to be made up will be resiliently supported and upwardly biased to the kelly joint. A winch having a cable and stabbing hook swings the kelly joint into position over the housing and vertically aligns it with the pipe joint supported by the housing.
Other U.S. patents of interest include U.S. Pat. Nos. 3,144,085, 3,212,578; 4,290,495 to Elliston; 3,662,842 to Bromell; 1,417,490 to Brandon; 1,908,818 to Brown; 2,142,022 to Volpin; 2,245,960 to Claire; 2,321,245 to Reed; 4,403,666 to Willis; and 4,591,007 to Shaginian et at.
In view of the foregoing, it is apparent that a need exists for improvements in the procedures and equipment available in top drive drill rigs to enable more efficient and effective assembly of multi-joint stands of drill pipe while top drive drilling procedures are occurring. Such improvements desirably should include procedures and devices which take maximum advantage of gravity to significantly reduce, if not eliminate, the need for manual handling of single and plural pipe joints. Also, the improvements desirably should include techniques and equipment for accurately and efficiently aligning the pin and box ends of two joints to be connected and for threading those joints together with known levels of torque. Further, the equipment should be maximally workable and useful with existing drill rig arrangements and procedures to avoid clutter on the drilling platform and to reduce the need for retraining of rig personnel. Further, the equipment providing the desired improvements should be compatible with, and able to co-exist with, rotary table drilling arrangements and procedures which have advantage under certain drilling conditions.